MODELING THE SPECTRUM OF WC-TYPE WOLF-RAYET STARS

Model calculations for carbon-rich Wolf-Rayet stars (WC) are presented which account for complex model atoms of helium and, especially, of carbon. The multi-level non-LTE radiation transfer in expanding atmospheres is simulated under the standard assumptions of spherical symmetry, homogeneity and stationarity. A small set of models is presented, and the dependence of the resulting spectra on the basic stellar and atmospheric parameters is studied. The synthetic spectra are compared with the observed spectrum of WR 111 (alias HD 165763, subtype WC5), identifying the numerous lines and blends and discussing their significance for the purpose of spectral analyses. The models seem capable of reproducing the observation with reasonable accuracy. Thus we have prepared the tools for future quantitative analyses of WC spectra. The theoretical spectra are found to depend not on the stellar radius R* and the mass-loss rate M individually, but (in good approximation) only on the ratio R*/M2/3. This "transformation law" which is already known from pure-helium models is confirmed here for the carbon lines as well.